Temporal distribution of suicide mortality: A systematic review

Highlights

• Suicide is a complex public health problem and the leading cause of premature death.

• If a clear seasonal pattern is identified, interventions can be better planned.

• Monday is the day with the highest frequency of suicide.

• Months of Spring and early Summer were the highest frequencies of suicide.

• The component most strongly related with changes in mortality rates was age.

Abstract

Background

suicide is a problem with world impact and the leading cause of premature deaths. The study of its distribution over time can bring a changed understanding of parameters attributed to, and the prevention of, suicide.

Aim

to identify the temporal pattern of suicide by systematic review.

Methods

Pubmed (Medline), LILACS, Virtual Health Library (VHL), Science Direct and Scopus (Elsevier), Web of Science (Thomson Reuters) and PsyNET (APA) were searched, using suicide-related descriptors and terms, for observational epidemiological studies of the temporal distribution of suicide. The review protocol was registered in PROSPERO (CRD42016038470).

Limitations

The lack of uniformity in reporting or standardisation of methodology in the studies selected, hindered comparison of populations with similar socioeconomic and cultural profiles, considerably limiting the scope of the results of this review.

Results

forty-five studies from 26 different countries were included in this review. Clear seasonal patterns were observed by day of the week, month, season and age-period-cohort effects. Few studies studied by trend, time of day or day of the month.

Conclusion

the review findings provide further evidence of substantial temporal patterns influenced by geographic, climatic and social conditions.

Introduction

Suicide is a complex public health problem and the leading cause of premature death (Mars et al., 2014, Turecki and Brent, 2016). It is also an event that belongs to one of those research domains where much is known, but not enough is understood (Ajdacic-Gross et al., 2003). The world impact is one death every 40 s or just over 800 000 deaths worldwide in 2012 representing an annual global age standardized suicide rate of 11.4 per 100 000, the second leading cause of death among 15–29 year olds, and 15th-most common cause of death worldwide (World Health Organization, 2014). This disorder produces such repercussions that the World Health Organization's Comprehensive Mental Health Action Plan sets a target of 10% reductions in countries’ annual rates by 2020 (World Health Organization, 2013).

Suicidal behaviour is strongly associated with conflicts, disasters, violence, abuse, feelings of isolation (Turecki, 1999), feelings of hopelessness and helplessness, stress and distress (Kaplan et al., 2002, Parente et al., 2007, Sá et al., 2010), sleep disorders, including insomnia (Pompili et al., 2013), mood disorders, mental disorders (including schizophrenia, personality disorders, addiction), impulsivity, alcoholism or drug abuse, anorexia, anxiety and depression (Asirdizer et al., 2010; Pretti and Miotto, 1998). Many others factors may contribute to suicide, as economic problems, the loss of a loved one, conflicts in the family, employment and problems at work, somatic illness, and honor (World Health Organization, 2002).

In the past fifty years, suicide rates have increased significantly (60%) worldwide (Macente and Zandonade, 2011, Parente et al., 2007). These rates are unevenly distributed by country, sex, age group and method used (Minayo et al., 2012). Most suicides occur in low- and middle-income countries, where resources and services for early identification, treatment and support of people in need are often scarce and limited, if indeed they exist (Saxena et al., 2014). In addition, suicide rates tend to be under-notified because of weak surveillance systems, misattribution of suicide as accidental death, as well as the criminalisation of suicide in some countries (World Health Organization, 2013). One of the fields that has most attracted researchers’ attention is temporal variation in suicide (Law and De Leo, 2013). In 1879, Morselli made a comparative study of the monthly distribution of suicide in 17 European countries from 1827 to 1877, noting that the number of suicides increased constantly from the beginning of the year until June, then declined constantly until year end. From the biological standpoint, the hypothesis is that temperature, or more precisely climate factors, provide the mechanism that enhances the vulnerability of the nervous system, thus increasing suicide frequencies in the Spring and early Summer, which he attributed to a direct influence on the circuits of the brain of climatic variables, in particular temperature (Morselli, 1879).

The hypothesis is that the seasonal variance in suicide depends on an underlying seasonal biological variance, influencing the control of impulses, as well as the serotonergic circuit (Maes et al., 1995). Brain levels of serotonin are sensitive to climate change, with variations which are a negative reflection of the seasonal distribution of suicide (Brewerton, 1989, Maes et al., 1995). One possible explanation is the existence of interaction between sunlight and the neurotransmitter serotonin, which affects and helps regulate mood. This means that exposure to sunlight can alter the levels of serotonin and influence behaviours and emotions such as mood, impulsiveness and aggressiveness (Vyssoki et al., 2014).

From another viewpoint, in the nineteenth century, Durkheim studied the distribution of suicides over the course of the year and by times of day. He claimed that the hotter months produced more suicides and that the highest frequencies were during the daytime. He developed sociological arguments assuming that higher levels of social activity in the spring and summer months lead to heightened social tensions and, accordingly, to a seasonal peak in the second quarter of the year, corresponding to Spring in Europe (Durkheim, 1897).

Known as seasonality, this phenomenon can be approached three ways: by main seasonal cycles (seasons and months of the year); seasonal patterns in minor monthly or daily fluctuations; and secondary effects involving public holidays or birthdays (Ajdacic-Gross et al., 2010). Studying these offers an important pathway to understanding the determinants of suicide and assists prevention endeavours (Christodoulou et al., 2012, Christodoulou et al., 2009). In order to improve these endeavours, it is essential to understand national, regional and local suicide patterns better, and absolutely crucial to understand the underlying mechanisms (Ajdacic-Gross et al., 2008a), including temporal distribution.

The research question here is: how are deaths from suicide distributed? The goal is to identify the temporal behaviour of this type of cause of death in the whole population of a region or territory.